The hypothesis underlying this proposal is that a family of transcription factors, the C/EBP family, originally isolated from liver has a key role int he differentiation of the lung epithelium. Members of the C/EBP family are known to play an important part in cells exhibiting specialized lipid metabolism. In addition to liver, C/EBPs alpha, beta and delta have been shown to have a role in adipocyte differentiation. RNA for these C/EBPs is also present int he lung. Preliminary data indicates that, in adult rat lung, C/EBPs alpha and beta mRNA and C/EBPs alpha, beta and delta protein are substantially enriched in type II cells. When the cells are removed from the lung and purified, the protein level rapidly declines. However, when the cells are plated on a matrix which restores SP-B, C/EBPalpha expression also returns. In fetal rats, mRNA for C/EBPalpha becomes detectable between days 18 and 20 of gestation, correlating with the maturation of the surfactant system and the appearance of detectable amounts of SP-A mRNA. Levels of C/EBPalpha protein also increase substantially at about day 19 of gestation. C/EBPalpha protein is detectable by immunodot blotting in NCI-H441, a lung-derived cell line which expresses SP-A and SP-B, but not in A549, which does not express the surfactant proteins. Transfection of A549 cells with C?EBPalpha induces SP-A gene expression while transfection of NCI-H441 cells with antisense against C/E PBPalpha reduces SP-A gene expression. In human fetal lung explant culture, treatment with cAMP and dexamethasone appeared to increase levels of C/EBPs beta and especially delta in nuclei of cells lining the alveoli. These data suggest the involvement of the C/EBP family in lung epithelial cell differentiation. The proposed experiments will: 1) characterize athe expression of C/EBP proteins in the developing normal lung and in the bronchopulmonary dysplasic lung; 2) evaluate the effect, on C/EBP proteins, of treatments which accelerate (cyclic AMP, dexamethasone, T3) or decelerate (phorbol ester, hypoxia) lung development; 3) study the effect of modulating C/EBP levels on development of cultured lung and 40 analyze the role of C/EBP proteins in activating transcription of the P-B gene promoter.